This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0064057, filed on Jul. 15, 2005, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to an organic compound that includes at least one difluoropyridine group in its molecules. The organic compound may be used as an electron injection layer, an electron transport layer, a light-emitting layer, or a hole blocking layer of an organic electroluminescent device.
2. Discussion of the Background
Electroluminescent (EL) devices are self-emissive display devices with a number of advantages such as high visibility, a wide viewing angle, good contrast, and rapid response speed. The EL devices are classified as either inorganic EL devices that use an inorganic compound as the light-emitting layer material or organic EL devices that use an organic compound as the light-emitting layer material. Organic EL devices have superior brightness, driving voltage, and response speed compared to inorganic EL devices, and offer a polychromaticity effect. These advantages have encouraged a significant amount of research into organic EL devices.
One study by Kodak Co. (“Appl. Phys. Lett.” 51, 913 (1987)) describes a functionally separated, double-layered organic EL device that includes ITO as an anode material, a Mg—Ag alloy as a cathode material, a tris(8-quinolinolate)aluminum complex (Alq3) as an electron transport material and a light-emitting material, and a triphenylamine derivative as a hole transport material. The EL device has a luminance of about 1,000 cd/m2 at an applied voltage of about 10V. The organic EL device exhibits luminance characteristics that are superior to a conventional single-layered organic EL devices due to its stacked structure of electron transport material and hole transport material.
Generally, the structure of an organic EL device is obtained by adding a hole injection/transport layer or an electron injection layer to a basic stack structure of anode/organic light-emitting layer/cathode. The resulting combinations include anode/hole injection layer/hole transport layer/organic light-emitting layer/cathode, anode/hole injection layer/hole transport layer/organic light-emitting layer/electron injection layer/cathode, and anode/hole injection layer/hole transport layer/organic light-emitting layer/electron transport layer/electron injection layer/cathode. Various organic compounds may be used in this stacked organic EL device as an electron injection layer or an electron transport layer, for example, Alq3, oxadiazole, triazole, benzimidazole, benzoxazole, or benzothiazole. But none of these compounds are sufficiently bright or durable. Alq3 is the best conventional compound known, due to its good stability and high electron affinity. However, the use of Alq3 in a blue light emitting device lowers color purity due to emission by exciton diffusion. Furthermore, organic EL devices that use conventional organic compounds consume too much power and an organic compound that requires less power is needed to increase the life expectancy and efficiency of organic EL devices.